Originally posted by downstairs no, i wanted to try and run 4ohms some way into my 8 ohm cab, what woulda happen?

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You do not 'run Ohms into a cab'. Ohms is the measuring unit for the impedance of the cab.

An amp puts out power (Watts). The higher the impedance of the cab hooked to the amp, the lower the power output. (The cab 'impedes' the flow of current, so to say)

And if the impedance of the cab(s) is too low, too much current will flow and the amp will smoke off sooner or later.

With all-tube amps things are a little different: The cab has to match the head exactly. To be able to run the amp at different loads, there is either a selector switch or different speaker outputs for 8/4/2 Ohms.

Tube power amps had different transformer taps (connections) that allowed the tube output to run with various different speaker impedances. The intent is to closely match the power amp impedance to that of the cabinet.

A solid state power amp has no taps. It is designed to operate with a specificed minimum impedance, and works fine with impedances higher than the specified minimum. For example, my QSC minimum impedance is 2 ohms. I run an 8 ohm driver and it is fine. If I had a tube power amp, I would use the 8-ohm tap to connect my 8-ohm cabinet.

Originally posted by bgavin Tube power amps had different transformer taps (connections) that allowed the tube output to run with various different speaker impedances. The intent is to closely match the power amp impedance to that of the cabinet.

A solid state power amp has no taps. It is designed to operate with a specificed minimum impedance, and works fine with impedances higher than the specified minimum. For example, my QSC minimum impedance is 2 ohms. I run an 8 ohm driver and it is fine. If I had a tube power amp, I would use the 8-ohm tap to connect my 8-ohm cabinet.